For many years, the conventional interpretation of the redshift in terms
of the Hubble expansion has met with occasional skepticism. Since the
time of the Bahcall-Arp debate on the redshift controversy in 1972
(Field et al 1973),
some issues (e.g. energy requirements for quasars,
infall into clusters) seem to have been resolved to the satisfaction of
most. On the other hand, although the evidence is largely
circumstantial, individual occurrences of alignments, apparent
associations, and extreme velocities may not be easy to explain via the
standard approach (e.g.
Arp 1987).

Tifft and coworkers (see
Tifft & Cocke 1989
and refs. therein) have
claimed that quantization effects are present in a variety of redshift
data bases, most notably in histograms of the radial velocity separation
of members of binary systems. Evidence for this periodicity, mainly the
manifestation of a 72.45 km s-1 harmonic, has also been
found, albeit not compellingly, in several different samples
(Sharp 1984,
Schneider et al 1986,
Croasdale 1989).
In examining the redshift distribution of
different populations of objects in the Virgo cluster,
Guthrie & Napier
(1990)
find no evidence for quantization in the redshift distribution of
dwarf irregulars, but a possible periodicity (slightly different from
Tifft's) appears in the power spectrum analysis of the brighter spirals.
This effect is significant only with the further assumption that the
Local Group is falling directly toward the Virgo cluster, as other
solutions will not give results with the same significance.

On the skeptical side of the issue,
Newman et al (1989)
point out the
statistical flaws of periodicity analysis in small-number samples, and
Sharp (1990)
further suggests that in the absence of statistically
significant confirmation, the claimed periodicity is not a physical
property of the galaxy pairs. In our opinion, redshift quantization is
not yet rigorously proved. However, the verification of redshift
quantization is potentially important because it does not fit within the
framework of conventional dynamics.